The present disclosure relates to a liquid lens and particularly to a liquid lens with improved transmittance and light collection efficiency.
There are variable-focus liquid lenses of related art that use change in interface between two liquids whose wettability is changed by voltage application so as to change the focal length. For such variable-focus liquid lenses of related art, there has been proposed a method for forming a cavity to center the liquids, as shown in FIG. 1A (see JP-T-2002-540464, for example).
As shown in FIG. 1A, a liquid lens 1 includes ribs 13 and 14, lower electrodes 15 and 16, an insulating film 17, a nonpolar liquid 18, a polar liquid 19, and upper electrodes 20 and 21 in the space between a transparent substrate 11 and a transparent top plate 12. The upper electrodes 20, 21 and the lower electrodes 15, 16 of the liquid lens 1 are connected via a power supply 31 and a switch 32. That is, when the switch 32 is turned on, a voltage from the power supply 31 is applied between the upper electrodes 20, 21 and the lower electrodes 15, 16. This voltage application changes the wettability of the nonpolar liquid 19, so that the shape of the interface between the nonpolar liquid 18 and the polar liquid 19 is changed and shaped into a curved convex lens. This shape of the interface focuses light that passes through the two-liquid layer. The curvature of the interface between the two liquids can be adjusted by adjusting the value of the applied voltage, allowing the focal length of the liquid lens 1 to be changed.
JP-T-2002-540464 describes how to center the liquids by forming and using a center-axis symmetric truncated cone-shaped cavity or an elongated groove-shaped cavity. That is, as shown in FIG. 1B, a circular cavity 41 is formed when the liquid lens 1 shown in FIG. 1A is viewed from the transparent top plate 12 side.
There has been also proposed a method for arranging such variable-focus liquid lenses of the related art in an array for use, as shown in FIG. 1C (see JP-A-2000-356708, for example).
For example, liquid lenses 1, each having a cavity 41 with a circular upper side, as described in JP-T-2002-540464 are arranged in an array as described in JP-A-2000-356708, so as to form a liquid lens array 51 as shown in FIG. 1C.
When light enters the liquid lens array 51, part of the light enters the portion indicated by the dotted line 52, passes through the liquid lenses 1-1 to 1-3, and is focused as indicated by the arrows shown in FIG. 2A.
However, among the light incident on the liquid lens array 51, the light incident on the portion indicated by the dotted line 53 does not pass through the cavities 41 of the liquid lenses 1-4 to 1-6, but is blocked as indicated by the arrows shown in FIG. 2B. Therefore, light transmittance of the entire liquid lens array 51 could be reduced.
Even when the portion other than the cavity 41 of each of the liquid lenses 1 is made of a material transparent to light, among the light incident on the liquid lens array 51, the light incident on the portion indicated by the dotted line 53 does not pass through the cavities 41 of the liquid lenses 1-4 to 1-6, so that it is not focused as indicated by the arrows shown in FIG. 2C. Therefore, the light collection efficiency of the entire liquid lens array 51 could be reduced.